Su-Jung Cho, Un Ju Jung, Hye-Jin Kim, Ye Jin Kim, Youngji Han, Byoung Seok Moon, Yong Bok Park and Myung-Sook Choi
Background: A high-fat diet (HFD) is thought to be one of the main environmental factors for obesity in which oxidative stress is an important pathogenic mechanism of obesity-associated metabolic syndrome including diabetes. Polyphenol-rich food plants are known to improve obesity-related diseases. The aim of this study was to investigate the effects of grape pomace (GP) and GP plus omija fruit (GPOF) on hyperglycemia and oxidative stress in diet-induced obese (DIO) mice. Methods: Male C57BL/6J mice were fed an HFD with GP (0.5%, w/w) or GPOF (0.5% GP plus 0.05% omija fruit, w/w) for 12 weeks. One gram of GP contains 0.26 mg of total flavonoid and 0.475 mg of total polyphenol, while 1 g of GPOF contains 0.2635 mg of total flavonoid and 0.491 mg of total polyphenol. Results: GP and GPOF significantly lowered fasting blood glucose level and insulin/glucagon ratio compared to HFD but increased plasma glucagon level. Supplementation with GP or GPOF improved glucose tolerance and the expressions of pancreatic insulin and glucagon while preserving α- and β-cells. GPOF in particular seems to improve insulin sensitivity by reducing plasma insulin and homeostasis model assessment of insulin resistance levels. Erythrocyte glutathione peroxidase and glutathione reductase activities were significantly lower in the GPOF group than in the HFD group along with decreases in erythrocyte hydrogen peroxide and thiobarbituric acid-reactive substance levels. Conclusion: These results suggest that GPOF, which is rich in flavonoids, may be beneficial in preventing an increase in the risk factors for diabetes in obesity, including fasting hyperglycemia, glucose intolerance, and oxidative stress.